SACRAMENTO, California (CNN) -- For more than two years, undercover cops on the Sacramento Police Department's vice squad have been working one of the most draining beats: trying to crack down on online child prostitution.

Police have nabbed nearly 70 girls under the age of 18 since 2005. Most of the girls were released to foster or group homes. Those are just the official figures; investigators think there are many more child prostitutes out there.

It is no easy task.

"We're asking these girls to do a big thing ... which is to stop what they're doing," said Sgt. Pam Seyffert of the Sacramento Police Department. "Stop what's working for them. Surviving is basically what they're doing."

Sacramento police are working with the FBI as part of a nationwide campaign to combat underage prostitution called Innocence Lost. The goal of the program, which is now in almost 30 U.S. cities, is to decriminalize the girls and concentrate on catching the pimps who control them.

"It really makes me angry," Seyffert said. "I think everybody on the team has different reactions to it, but I just flat out get really angry that some guy thinks he can take this girl and basically deprive her of her freedom."

Child prostitution is even tougher on the parents of these girls. Roslyn and Sergio's daughter had been missing for more than two weeks. They waited for hours at police headquarters in hopes that their daughter would be found.

Vice squad officers found her in a downtown apartment with Bruce William Carter, a 21-year-old man who police said had posed on the Internet holding fistfuls of cash. He pleaded not guilty to charges of statutory rape and was held in lieu of $35,000 bail.

The couple's daughter, who had just turned 17, was detained but not arrested.

"It hurt," said Roslyn, who appeared weary and a bit shell-shocked. "Because you don't want to see your children involved in things like this. You don't realize how dangerous the Internet is. Now, we got to keep her away from the Internet."

Police say most of the ads appear on Craigslist, the popular and free Internet classifieds site, under a category named "Erotic Services." Even though Craigslist has posted a bold disclaimer warning against human trafficking and the exploitation of children, law enforcement officials said it doesn't seem to deter girls from posting the ads or men who are searching for sex.

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To help answer that question, Sacramento police made arrangements for CNN to interview a 14-year-old girl who said she'd started selling herself as a prostitute at the age of 11.

"I wanted to feel loved. ... I wanted to feel important," said the teen, who did not want to be identified.

She said she used Craigslist because it was free and she could post dozens of ads a day. Even though she understood the seriousness of what she was doing, she said she didn't care.

"You could put stuff in your ad like 'wet and wild,' 'fun and sassy,' things like that to catch their attention, to make them want you," she said.

Craigslist executives said they abhor the fact that their site is being used for child prostitution but believe that the problem could be harder to track if they removed the category.

"It would be a bigger problem if we removed that category and had those ads spread throughout the site," said Jim Buckmaster, chief executive officer of Craigslist.

Both legal experts and police say Craigslist bears no legal responsibility. Undercover officers said the fact that the listings can be traced helps them pinpoint the girls and sometimes leads them to pimps.

For her part, Roslyn has a strong message for the man arrested in connection with her daughter's detention.

"I want him to stay away from my daughter," she said. "I'm going to put a restraining order on him. Every time he goes near my daughter, I'm going to call the police and have him put in jail."

Even though they have more work than they can handle, vice officers hold out hope that they can save more girls from a life of prostitution.